I always loved the civ style games, especially Masters of Magic. And I love the Myth series. I liked that it was 3d and played out as a 3d game (as apose to warcraft 3 that was 3d and played out like a 2d game). So I got to thinking, why not combine the two?

Have a complete 3d globe, like in X-com, and spread out like a civ game. I would say in real/relitive time like X-com, but I relize that 5 oponants moving 1,000 troops each would kill the frame rate... hell, it would kill the whole damn program. But the whole globe, randomly generated and unmapped until you crossed it. The world veiw I guess would just need to unfold based on turn based moves. But, the range of terrain could be awsome. Each with thier own benifits and natural resorces. And in a battle would need you to take advantage of all possible standpoints; archer take to the hills, artilery would avoid water, swords men would use the woods for cover, and heros could lead your men giving certain benifits to surounding men.

I would make it so you can't mount a creature until you capture it in the wilderness and start breeding them. Conflict of races among your people, until the culture accepts one another. The development of new arts could help out the masses to stay happy. Reseach tree for magic and a research tree for technology. Spies, are always cool. Diplomacy. Hire political figures to run your cities and have them give perks for different things. Grab any citizen to do any political or militatry leadership and base perks off they're job. Shift around the form of government to best suit your needs. Give heros thier own gear that alters thier abilities. Have mages work in groups and making formations to get a large effect. Oh! Oh! And make a system of gods so you have to appease them at all times. The gods could grant you certain gifts, like cool gear for your hero's.